J-dimethylbutane



Jan. 21, 1964 A, WORTHINGTON 3,118,299

METHOD OF ANALYZING SUBTERRANEAN FORMATIONS FOR HYDROCARBONS Filed Sept. 29, 1960 8 Sheets-Sheet 1 INVENTOR ALBERT 5. WORTH/NGTON J 1964 A. E. WORTHINGTON 3,118,299

METHOD OF ANALYZING SUBTERRANEAN FORMATIONS FOR HYDROCARBONS Filed Sept. 29, 1960 8 Sheets-Sheet 2 1--WATER COLOR ADDlTlVE COLORI- METER INVENTOR ALBERT E. WORTH/NGTO/V 1964 A. E. WORTHINGTON 3,118,299

METHOD OF ANALYZING SUBTERRANEAN FORMATIONS FOR HYDROCARBONS Filed Sept. 29, 1960 8 Sheets-Sheet 3 DRILLING FLUID RETURNS l INV ENTOR ALBERT E. WORTH/NGTO/V ,1 BY La).

A NEYS Jan. 21, 1964 A. E. WORTH INGTON 3,118,299

METHOD OF ANALYZING SUBTERRANEAN FORMATIQNS FOR HYDROCARBONS Filed Sept. 29, 1960 8 Sheets-Sheet 4 DEPTH BENZENE TOLUENE M-XYLENE IIIIIII'IIIIIIIIIIIIIIIII|II|IIIIIIIIII||I|| I I 1 I I I I I I llIlllllllllllllllllll'l FEET PARTS PER MILLION IN DRILLJNG FLUID FIG.4

INVENTOR ALBERT E. WORTH/NGTON -2 1964 A. E. WORTHINGTON 3,113,299

METHOD OF ANALYZING SUBTERRANEAN FORMATIONS FOR HYDROCARBONS Filed Sept. 29, 1960 s Sheets-Sheet 5 CARRIER GAS SOURCE HA I/ I 76 f f f DISTILLATION SEPARATING SAMPLE PARTITIONING H65 DETECTOR RECORDER INVE NTOR ALBET E. WOTH/NGTON 1964 A. E. WORTHINGTON 3,

METHOD OF ANALYZING SUBTERRANEAN FORMATIONS FOR HYDROCARBONS Filed Sept. 29, 1960 8 Sheets-Shet 6 LL. A

FIG.6

INVE NTOR ALBERT E. WORTH/NGTON ATTRNES 1964 A. E. WORTHINGTON 3,118,299

METHOD OF ANALYZING SUBTERRANEAN FORMATIONS FOR HYDROCARBONS Filed Sept. 29, 1960 a Sheets-Sheet 7 METHYLCYCLOHEXANE PLUS OTHER CYCLOPARAFFINS BRANCHED OCTANES OCTANES NORMAL HEPTANE AND OTHER HYDROCARBONS 2,3-DIMETHYLPENTANE S-METHYLHEXANE PLUS BENZENE '2- METHYLHEXANE METHYLCYCLOPENTANE CYCLOPENTANE PLUS S-METHYLPENTANE Z'METHYLPENTANE PLUS 2,3'DIMETHYLBUTANE 2.,2-DIMETHYLBUTANE CHROMATOGRAM A SIDE WALL SAMPLE NORMAL PENTANE FROM 1860 T.

TIME ON RECORDER CHART (VOLUME OF CARRIER GAS) ISOPENTANE FIG.7

AIR AND LIGHT GASEOUS HYDROCARBONS INVE NTOR ALBERT E. WORTH/NGTON START CONCENTRATION OF HYDROCARBON IN SAMPLE TIME ON RECORDER CHART (VOLUME OF CARRIER GAS) CONCENTRATION OF HYDROCARBON lN SAMPLE 1964 A. E. WORTHINGTON 3,118,299

METHOD OF ANALYZING SUBTERRANEAN FORMATIONS FOR HYDROCARBONS Filed Sept. 29, 1960 8 Sheets-Sheet 8 METHYLCYCLOH EXANE BRANCHED OCTANES NORMAL HEPTANE AND OTHER HYDROCARBONS 2,3-DIMETHYLPENTANE. 3-METHYLHEXANE PLUS BENZENE Z-METHYLHEXANE METHYLCYCLOPENTAN E NORMAL HEXANE CYCLOPENTANE PLUS a-METHYLPENTANE Z-ME'THYLPENTANE PLUS 2,3'D1M ETHYLBUTANE 2.2-DIMETHYLBUTANE CHROMATOGRAM B SiDE WALL SAMPLE NORMAL PENTANE FROM 2196 FT.

ISOPENTANE FIG. 8

AIR AND LIGHT GASEOUS HYDROCARBONS INVENTOR ALBERT E. WORTH/NGTON sTAR-r BY fi Z. LANCE a N s United States Patent EEETHOD 9F ANALYZWG SUBTERRAYIEAN FGR- 1 MATE N FQR HZDRQQIARBGNS Alb-er E. Worthington, Lagnna Beach, Crdit., assignor to Californ a Research Corporation, San Francisco, Cfl'hfi, a corporation of Delaware Filed Sept. 29, 1960, Ser. No. 59,2ti9 17 Claims. (Cl. 73-23) The present invention relates to a method of logging subterranean formations penetrated by a well here to determine the presence therein of certain hydrocarbons, and more particularly to a method of examining samples obtained from subterranean formations to detect the presence therein of commercially valuable hydrocarbons containing molecules having at least five carbon atoms and having a boiling range of about 25 C. (77 F.) to 180 C. (350 F.) and known as gasoline fraction hydrocarbons.

This application is a continuation in part of application Serial No. 644,224, filed March 6, 1957, entitled Drilling Fluid Logging, now abandoned.

Heretofore, in examining samples of earth formations contained in drilling fluid returns to obtain indications of penetration of oil-bearing rocks, it has been the practice to examine such fluids and/or cuttings by one or both of two common methods.

One of these methods includes the examination of the drilling fluid returns for the presence of gases, such as methane, ethane, and the like. in this type of system, the drilling fluid or cuttings is subjected to agitation, evacuation, and/or aeration, and the vapors of the light hydrocarbons mixed with air are drawn off and sampled. The presence of hydrocarbons in this air stream is indicated by measurement of the electrical conductivity of a hot Wire, said hot Wire serving as a catalyst for combustion of the gas-air mixture, thus causing the temperature of the Wire to increase so that the presence or absence of hydrocarbon gases in the air is indicated by an increase or decrease in electrical conductivity of the hot Wire. By adjusting the temperature of the hot Wire, either methane alone or methane plus ethane and higher molecular Weight hydrocarbons can be detected.

The abundance of methane gas is found to be much greater than that of ethane and other higher molecular weight gases. Even though the determination of methane by the hot-wire method is quite accurate, the determination of ethane and higher is thus inherently inaccurate because of the necessity of determining a small difference between two large numbers.

Unfortunately, also, high accuracy of measurement of methane is not warranted as a method of exploring for commercial petroleum accumulations, since dry gases consisting mostly of methane are frequently encountered in the earth in locations such as peat beds, coal seams, shales, dry-gas sands, and the like; thus, in normally favorable sedimentary rocks, traces of such gases occur many times without any relation to accumulations of commercial oil. For this reason, the accuracy of the measurement of methane does not indicate the presence or absence of commercial oil, and in part it can be misleading as to the need for performing formation fluid tests, either While drilling or after the Well has been completed. Such formation tests are quite expensive in the total cost of drilling a well. Such high cost is due in part to the fact that it is usually necessary to set steel casing and achieve a suitable cement bond to seal the casing to the borehole.

The second method of drilling fluid logging common in field practice is to inspect the drilling fluid returns with ultraviolet ligh. The purpose of this inspection is to detect the presence of fluorescent materials that frequently are present in oil accumulations in the earth. Unfortuftldihd "ice nately, such fluorescent materials are also frequently encountered in other substances, not containing gasoline fraction hydrocarbons, such as those found in tar streaks and other petroleum deposits Where all of the lighter components, specifically those that make an oil accumulation commercially interesting, have been lost or have migrated away from the deposit. Various minerals, oils, greases, and such, used in the drilling operation, or even in the drilling fluid, may also be fluorescent. Accordingly, ultraviolet light inspection of the drilling fluid returns gives a far greater number of oil indications than the true number of potentially commercial petroleum deposits. Thus, ultraviolet methods for inspection of drilling fluid returns are as unsatisfactory for finding commercially valuable oil accumulations as the methane gas analysis system outlined above.

In contrast to the prior art methods of logging drilling fluid returns, 1 have found that the presence of significant quantities of gasoline fraction hydrocarbons in the drilling fluid returns provides a good indication and basis for distinguishing between commercial oil and dry gas or Worthless remnant petroleum deposits. By gasoline fraction hydrocarbons are meant those hydrocarbons usually separated commercially as straight-run gasolines, i.e., hydrocarbons with at least five carbon atoms per molecule and usually having boiling points lying between about 25 C. (77 F.) and C. (350 F.) at atmospheric pressure. Hydrocarbons of more than 12 carbon atoms are not usually present in more than insignificant amounts. Further, the gasoline fraction hydrocarbons of concern in the present invention normally do not fluoresce sufficiently to permit the use of fluorescence as an analysis method for the very small amounts in aqueous systems, such as in drilling fluid returns.

In particular, this invention contemplates analysis of samples of subterranean formations, including samples obtained in drilling fluid returns, for one or more of the gasoline fraction hydrocarbons entrained or contained in such samples. This analysis includes identifying said gasoline fraction hydrocarbons by molecular species and determining the presence and/or relative abundance of said gasoline fraction hydrocarbons as an indication of the presence of commercially valuable oil in these formations.

In analyzing drilling fluid returns, for example, I have found that an increase in the content of gasoline fraction hydrocarbons in the drilling fluid indicates the approach of the borehole to oil accumulations, sometimes as far ahead as 200 feet above the oil zone. This indication can be attributed to the occurrence of very minute upward extensions of the oil accumulations. These extensions may take the form of small oil-filled sand lenses and/ or fissures in the reservoir cap rock, said extensions being too small to be recognized from electric logs or other conventional formation evaluation procedures.

I have found that of the gasoline fraction hydrocarbons (which include normal and branched-chain paraflins, cycloparaffins, aromatics, and parafiinically substituted cycloparafi'ins and aromatics), those having five to eight carbon atoms are preferred for the practice of my invention, since the amounts of these hydrocarbons appear to be the most significant indicators. Illustrative of the preferred hydrocarbons are isopentane, pentane, benzene, toluene, ortho-, metal-, and paraxylenes, ethylbenzene, cyclohexane, methylcyclopentane, methylcyclohexane, l, B-dimethylcyclopentane, normal hexane, normal heptane, and normal octane. Of these, the aromatics of six to eight carbon atoms are especially preferred in most instances because of the ease of analysis, particularly when the analysis is made by infrared absorption procedures. However, when the method of gas liquid partition chromatography is applied to analyze the constituents, the procedure conveniently be extended to include all the possible parallins, branched paraffins, cycloparaflins, aromatics, and mixed hydrocarbon molecules, having from five to ei ht, inclusive carbon atoms, to produce a corresponding increase in the clarity of the interpretation of the analysis.

More especially, my invention is directed to a method of logging samples of subterranean strata obtained from a wel bore, which samples may be contained in drilling fluid returns or obtained by side wall samples of the subterranean strata exposed in the well bore. The earth samples from the well bore are analyzed preferably for the lower aromatic hydrocarbons, such as benzene and its derivatives, containing seven and eight carbon atoms, which I have found to be excellent indicators of commercial oil deposits. 1 have further found that the relative proportion of benzene to toluene and Xylenes in drilling fluid returns provides a practical method of distinguishing commecially valuable oil from less valuable dry gas and worthless remnant petroleum deposits. When gas liquid partition chromatography is employed as part of the analyzing apparatus, preferably the gasoline fraction hydrocarbons, which include normal and branched-chain parafiins, cycloparaffins, aromatics, and paraffinically substituted cycloparatiins and aromatics as mentioned heretofore, are obtained, and the distinction of commercially valuable oil from dry gas or residual petroleum accumulations can then be more advantageously determined by considering the relative abundance of specific parafiinic or cycloparatlinic compounds. For example, one can use the ratios of iC to C 11% to nC or the sum of the lower boiling components, such as C to C inclusive, divided by the sum of the higher boiling components, such as C to C inclusive, for this purpose.

in carrying out the present invention, I have found it most preferable to subject the samples being analyzed to distillation at substantially 100 C. (212 F.) and atmospheric pressure with the addition of gas, such as air or steam, and/ or other material which aids the volatilization of the gasoline fraction hydrocarbons (as defined above) contained in the sample. When drilling fluid returns are being analyzed, this distillation may be performed batchwise or continuously from the drilling fluid stream it self, or a portion thereof, from the cuttings, or from a composite sample thereof. Vfisere the sampling of rill ing fluid returns is discontinuous, the frequency of sampling will depend on the ..kelihood that the formation being penetrated will contain oil accumulations, the drilling rate, economic considerations, and other factors. In some instances, sampling at intervals of 25 to 50 feet Will be sufficient. Drilling fluid returns are defined, for the purposes of the present invention, as liquid or oth r fluid used for drilling, drill cuttings contained therein, gas or fluid phases trapped or entrained therein, the formation fluid itself, or any part or combination of parts thereof returning to the surface from the borehole while iiling or associated with the act of drilling, conditioning, or otherwise operating in the Well bore.

Under some circumstances, the mechanical operation of d ing in a well bore may be less than ideal, especially the point of VlGW of drilling fluid logging. Some combinations of drilling methods, drilling fluid properties, and formation rock characteristics may result in the sloughing or caving of formation into the borehole after passage of the drill bit. This sloughing may continue after several hundreds or even thousands of feet of hole have been drilled beyond the incompetent formation. It the sloughing formation is hydrocarbon bearing, then the drilling fluid system may be severely contaminated by the process, rendering difficult the correlation of any kind of data obtained from the mud stream with the specific horizon in the Well bore. In other circumstances, contradictory evidence exist as to the probable commercia oilbearing potentialities of a specific horizon after drilling has proceeded past that horizon and after employing conventional logging devices.

In such circumstances as those mentioned above, as well as in other circumstances Where specific information is desired about a particular subterranean stratum, the technique of side Wall sampling is employed to obtain formation samples to be analyzed. In one method for obtaining such samples, a hollow metal bullet is fired by explosive means from a gun controlled from the surface and accurately located in the well opposite the horizon of intere t. e bullet penetrates the formation a few inches, but remains attached to the gun through a stout cable. The bullet and the sample contained in it are re moved from the formation by pulling on the gun, and the gun together with the attached bullet and contained sample is raised from the well bore to the surface. The one or two cubic inches of the formation obtained in this manner commonly is referred to as a side Wall core or side Wall sample.

Other devices are known to the art for obtaining cores or formation samples from a Well bore, particularly devices Which permit samples of the formation by operations performed through special d ing collars or subs designed for this purpose. Also, in some cases a core may be obtained from a formation of interest through the usual coring procedures while the borehole is being dri led through this formation.

Regardless of how the formation sample is obtained, for the purpose of the analysis of the present invention such a sample can be considered as a somewhat-largerthan-usual chip, such as one normally obtains from the drilling mud stream during the drilling operation, but unlike a regular drilling chip such a sample can be accurately assigned to a specific horizon in the Well bore. The analytical procedure employed is substantially the same, whether a sample of drilling fluid is being analyzed or a formation sample obtained by some other means. It usually is desirable to crush the core or side wall sample in some manner prior to the distillation step, as will be explained more fully hereinafter.

The method of this invention preferably uses steam or other volatilizing assistant that is both gaseous at the distillation temperature and can be removed before, or does not interfere in, the subsequent analytical method. By such means, the small amount of gasoline fraction hydrocarbons contained in the formation sample is readily volatilized and separated in the vapor state from the bull; of the sample. Thereafter, it can be recovered, along with the volatilization assistant, by condensation. Preferably, an inert volatile solvent for the gasoline fraction hydrocrabons of interest is advantageously employed in addition to the steam. Such a solvent may, by Way of example, be isooctane or toluene or some other material which meets the requirements of the separation and analytical procedures of this invention. To illustrate one of the desired characteristics of an added solvent material, at the temperature of steam distillation iso-octane is distilled with the gasoline fraction hydrocarbons and collects in the distillate as a separate phase in whic the gasoline fraction hydrocarbons dissolve. As indicated above, the iso-octane or other simflar material must be sufficiently pure and otherwise selected not to interfere With the subsequent analysis.

To illustrate more specifically the process of steam distillation as used in the present invention, a sample of the drilling returns is placed in a suitable vessel. Additional Water may be added in the case of very viscous samples, or where cuttings are used. The addition of salt is frequently beneficial when the mud is very thixotropic, and in some muds Where severe foaming may be encountered the addition of antifoaming agents is desirable.

Steam is admitted to the vessel near its lowest point. Steam is bubbled up through the sample so that it heats and stirs it in the process. An additional source of heat may also be applied directly to the vessel, if desired, to speed up the process. When the sample and vessel are sufiiciently hot (and this may sometimes occur without added heat with drilling fluid returns from deep, hot wells), vapors will arise from the sample and leave the vessel by means of a suitable exit which leads to a cool condenser where said vapors are condensed to the liquid state and caught in a suitable receiver.

The vapors leaving the sample and accumulating in the receiver will consist mostly of water. Any hydrocarbons, such as benzene (boiling point 80.1" C.), hexane (B1 68.7 C.), and heptane (13.1. 98.4" C.) will also pass rapidly into the vapor state when the temperature of the sample reaches their boiling point. I have found in addition that other hydrocarbons, such as toluene (B.P. 11[).6 0.), ethylbenzene (8.1. 136.2 C.), orthoxylene (3.1. 144.4 C.), meta-xylene (BP l39.1 C.), and para-xylene (BF. l38.4 C.), are also vaporized in substantial amounts when they are present in the sample, even though the sample temperature does not exceed approximately 100 C.

Steam distillation has several advantages over ordinary distillation. First, the incoming steam violently agitates the sample and brings about rapid equilibrium between the liquid and the vapor. Secondly, gasoline fraction hydrocarbons boiling at temperatures substantially higher than that of water can be effectively concentrated by this method without distilling essentially all of the water from the sarnple, as would be necessary in normal distillation.

There are some circumstances in which ordinary distillation may be preferred over steam distillation. For instance, when the analytical technique employed to analyze the material separated from the drilling returns is unable to distinguish between benzene and other aromatic hydrocarbons, and when this distinction is desired, then it may be desirable to separate benzene alone from the drilling fluid returns. Alternatively, when diesel oil is used as a component of the drilling fluid, for reasons well known to the drilling art, it is found that the drilling fluid contains large amounts of toluene and higher molecular weight substituted aromatic hydrocarbons originating from the diesel oil and interfering therefore with the interpretation of the resulting data. All samples of diesel oil that I have examined contain these materials, although the nominal, minimum boilin point of diesel oil is about 175 C. at atmospheric pressure, and it should not therefore contain these materials.

The concentration of benzene in three diesel oils 1 have examined is close to six parts per million and hence, when comprising about percent of the drilling fluid by volume, contributes a small background in the subsequent analysis of less than one part per million.

ii/hen conditions such as these prevail, fractional distillation can be used to preferentially isolate only those gasoline fraction hydrocarbons boiling below 100 C. A mixture of drilling returns, sufficient water, and a suitably inert, but volatile, material, such as iso-octane, can be heated together in a vessel and refluxed to attain equilibrium as desired. The material in the vessel is then carefully distilled, preferably through a distillation column having a few theoretical plates, until all the isoctane, which boils at 99 C., has distilled over, and the temperature of the vapors leaving the top of the column starts to rise toward 100 C. At this point heating is discontinued, and the resulting sample, containing only isooctane and the gasoline fraction hydrocarbons boiling below 100 C., is analyzed as hereinafter detailed. However, when gas liquid partition chromatography is used for analysis, fractional distillation of the hydrocarbons boiling below 100 C. may still leave in the concentrate to be analyzed a suflicient amount of the gasoline fraction hydrocarbons derived from the diesel oil to interfere with the accuracy of the subsequent analysis. This problem can be avoided by not using diesel oil or other gasoline-containing materials in the drilling fluid, but using instead a hydrocarbon material which is substantially free or the gasoline fraction hydrocarbons pertinent to the analysis of this invention.

As indicated above, the drilling fluid returns are subected to distillation advantageously in some instances with the aid of steam together with an inert but volatile material. When infrared analysis is to be employed, iso-octane is a preferred volatile material for this purpose. l have found that the iso-octane should be added to the formation sample, which may be a sample of drilling fluid returns, prior to the beginning of the steam distillation. The distillation is continued until all of the iso-octane has been collected in the receiver where it occurs as a separate phase from the water. Thereafter the two phases in the distillate may be readily separated. In practice, I have found that this method can be made more rapid and more eflicient in concentrating the gasoline fraction hydrocarbons boiling at a higher temperature than water by placing a reflux condenser on the vapot outlet of the distillation vessel and by allowing the mixture of sample water, steam, and iso-octane to be thoroughly mhred and reach an equilibrium under refluxing conditions before taking overhead any distillate and collecting the distillate in the distillation receiver.

When gas liquid partition chromatography analysis is employed, 1 have found that toluene is a preferred volatile material to be used. Although the toluene may be employed in the manner of the iso'octane, as described above, preferably in preparing the distillate for this analysis the disti lation of approximately 500 milliliters of the formation sample is initially permitted to proceed without the addition of the solvent material until a small amount, approximately 25 cc., of distillate is recovered. A portion of the toluene, approximately 2 cc., is then placed in the vessel with the formation sample, and the distillation is allowed to proceed until a further portion of distillate, approximately cc., is recovered. A further amount, approximately 2 cc., of toluene is then placed in the vessel containing the aforementioned sample, and distillation proceeds until the total amount of condensate is approximately cc. At this time, substantially all of the added toluene with the gasoline fraction hydrocarbons from the formation sample dissolved in it will be in the condensate. As with the iso-octane described previously, the toluene and the hydrocarbon fractions that it has dissolved occur as a separate phase from the water in the condensate, and the two phases may be readily separated.

The distillate obtained from the foregoing distillation, or a convenient portion thereof, is subjected to analysis for the selected gasoline fraction hydrocarbons.

Gccasionally during drilling a mechanical mud degasser may be used to remove gaseous or volatile materials from the drilling fluid in order to control the mud weight. The usual principal constituent evolved from the mud in a degasser is methane. The volatilizing methane will assist the volatilization of the gasoline fraction hydrocarbons sought as indicators of commercial oil as well as a certain amount of water. It is apparent, therefore, that when a degasser is used the gaseous efl'iuent from this degasser will correspond approximately to the vapors evaporated from the drilling fluid during the steam distillation previously described. Hence, the method of the present invention may be modified to be used with a degasser by condensing the gaseous effluent preferably to which has first been added a small amount of solvent carrier. The condensate will thus consist of two phases, the solvent carrier and water, and the volatile methane gas will pass from the system. The solvent carrier phase can then be separated from the water and treated as in one of the manners to be described.

Analysis of the distillate or condensate containing concentrated therein the gasoline fraction hydrocarbons can be performed in any one of several ways. In accordance with one method of carrying out the analysis, as indicated heretofore, the gasoline fraction hydrocarbons in the distillate will be found dissolved in an organic solvent which acts as a carrier iluid. As mentioned heretofore, I have found that iso-octane (i.e., 2,2,4-trimethylpentane) is an ideal solvent and carrier fluid Where infrared analysis is to be employed. -f the selected hydrocarbons are obtained in the distillate as a water solution or mixture, then they can be extracted from the distillate with iso-octane, such as by agitating said water solution with a small volume of iso-octane. After settling into two phases, the iso-octane phase is separated from the Water phase and then preferably dried chemically, for example, with anhydrous calcium sulfate. When gas liquid partition chromatography analysis is to be performed, and toluene is used as the solvent carrier, then mechanical separation of the two phases is suflicicnt.

The dried solution is then placed in the sample cell of a dual-beam infrared analyzer, such as the Model 21 instrument manufactured by the Perkin Elmer Corporation of Norwalk, Connecticut. The reference, or standard cell, is filled with pure iso-octane. The infrared spectrum is then scanned from 12.5 to 15 microns, and a record of the absorption spectrum is obtained. 1 have found that using cells 0.4 inch in thickness (measured between the inside faces of the sodium chloride windows of the cells), I can detect 9.2 part per million of ben zene in iso-octane and two parts per n- --on of toluene and other similar substituted aromatic hydrocarbons. Such high sensitivity is usually not required, and 0.2- inch cells are usually convenient.

The identification of the kind and concentration of the preferred aromatic hydrocarbon constituents is based upon measurement of the optical absorbance at the following Wave lengths:

The determination of ethylbenzene is not as precise as that of the other constituents, due to a more or less g neral aromatic absorption peak at 14.3 to 14.4 microns. As iso-octane has a minor peak at 13.43 microns, no useful information is obtained at this wave length, because the opacity of such a relatively great thickness of solvent causes too little energy to be transmitted to 1.16 detector for proper functioning of the apparatus. For this reason, the ortho-xylene peak at 13.48 microns is partially obscured and is useful ordy for qualitative identification.

Drilling fluids requently contain appreciable amounts of carbon dioxide which pass over into the iso-octane during the steam distillation. Carbon dioxide has a strong absorption peak at 15.15 microns which tends to interfere with, but not obscure, the benzene peak. Hence, preferably the carbon dioxide is removed in order to eliminate this obscuring eflect. For this purpose, the isooctane sample can be treated, after drying, with an agent such as Ascarite (a commercial preparation of sodium and calcium oxides suspended on asbestos). it should be noted that agents designed to remove water or carbon dioxide from the iso-octane solution by ph sical adsorption rather than chemical reaction should be used only with caution so as to avoid loss of some or all of the arcmatic hydrocarbons of interest in the absorbate.

Using this later technique, I have found that 100% of the benzene, 60% of the toluene, and 55% of metaxylene can be removed from a SOS-milliliter sample of a typical clay-base drilling fluid to 50 mi'liliters of water and 10 milliliters of iso-octane have been added by refluxing the mixture for ten minutes and then allo. ing the steam distillation to proceed for five minutes until all the iso-octane is carried over. The iso octane is then separated from the water and prepared for analysis by infrared spectroscopy as outlined hereinabove.

Hence, as described in detail above, one method of carrying out the present invention is to obtain from drilling fiuid returns or other formation samples evaporates containing at least a part of the gasoline fraction hydrocarbons contained therein and collecting such evaporates in a nonaqueous solvent such as iso-octane or other material that does not mterfere with the subsequent analysis. Then, when required, the solution of gasoline fraction h- 'ocarbons is dried and preferably also freed of carbon d.oxide. Thereafter the solution is subjected to infrared spectroscopy to determine at least m aromatic hydrocarbon, preferably one having six to eigrt carbon atoms. As indicated above, the determination is made by measuring the infrared absorption at wave lengths indicative of the selected aromatic hydrocarbons. Changes in the selected aromatic are correlated with depth of the freshly exposed formation contacted by the sample of drilling fluid returns which showed the change.

in accordance with another method of carrying out this analysis, the Water solution or distillate mixture containing the gasoline fraction hydrocarbons obtained by simple steam distillation Without addition of a carrier is then exposed to high-energy ionizing radiation, such as, for instance, the gamma radiation from a cobalt 60' source. This radiation forms free hydroxyl radicals in the water. These hydroxyl radicals undergo many reactions in the presence of hydrocarbons; in particular, they form phenol and phenolic derivatives from benzene and other aromatic hydrocarbons. The yields of phenol can be increased by the presence of oxygen dissolved in the Water.

Detection of phenol and phenolic derivatives in water is much easier than detection of aromatic hydrocarbons because the detection may be performed with less expensive instruments in aqueous solution. However, the reactions used in the detection are not nearly as specific for individual aromatic compounds as are the infrared absorption peaks. Any one of several reactions may be employed to convert the phenol to a colored derivative.

For example, the method of Folin-Denis may be applied, wherein, to the phenol-containing solution is added a mixture of phosphotungstic and phosphomolybdic acids and an excess of sodium carbonate. The solution is then slightly warmed, allowed to stand twenty minutes, and the deep blue color caused by phenol is measured by visual comparison with standards or preferably in an automatic colorimeter set to the appropriate wave length.

Alternatively, the phenols may be determined by the 4-arninoantipyrine method. In this method, the sample is adjusted to a pH of 9.8 to 10.2 by the addition of ammonium hydroxide. Three percent 4-aminoantipyrine reagent is then added, followed by 2% potassium ferricyanide. The optical density of the resulting red color can then be determined at 51" millimicrons in an optical colorimeter or a visible spectrophotometer, such as the Beclzman Instrument Company Model DU or DK.

Alternatively, the aromatic hydrocarbons can be converted to phenols by the action of chemicals alone, such as hydrogen peroxide in the presence of ferrous iron (Fentons reagent), or by a combination of ultraviolet radiation and oxygen. In either case, an analysis of the resulting phenols would proceed by a similar course. Again, alternatively, the phenols formed in these reactions can be extracted from the aqueous solutions with ethyl ether and examined in the ultraviolet at 273.5 millimicrons for the characteristic absorptions of phenol.

In accordance With another method of carrying out the analysis indicated heretofore, and one that is preferred, the gasoline fraction hydrocarbons are extracted from the drilling fluid or formation sample by means of distillation assisted by the use of toluene as the volatile solvent carrier. The toluene and the gasoline fraction hydrocarbons dissolved therein are separated from the distillate, and a small amount of this concentrate is placed in a receptacle connected by a long capillary tube to the flash vaporizer of a chromatograph analyzer. The receptacle is placed under pressure. The capillary tube and the vaporizer are purged by forcing a portion of the concentrate through them to remove any traces of contamination or residue from concentrates previously tested, and the flash vaporizer is then connected to the packed columns of the chromatograph wherein the various gasoline fraction hydrocarbons of interest are separated. The chromatograph produces a record from which the identity and amount of each of the constituents of interest in the concntrate can be determined, as will be explained in more detail hereinafter.

For convenience of description, I have described this operation as being performed in a batchwise manner, either on samples of return drilling fluid, drill cuttings, or formation samples obtained in some other manner. Continuous countercurrent methods of steam distillation, or steam stripping, as it may be called, can also be used where a continuous sample is desired, as in the logging of drilling fluid returns in conventional rotary drilling. This in no way implies that continuous analysis methods cannot be employed, and in fact under some circumstances such continuous analysis is to be preferred.

After the analysis for gasoline fraction hydrocarbon content of the evaporates from the formation sample, the changes in such content from sample to sample, as indicated above, are correlated with the respective depths of the subterranean formations from which the samples were taken. For example, when drilling fluid returns are being analyzed the changes in the content of gasoline fraction hydrocarbons are correlated with the depths of the freshly exposed formations in contact with the samplings of drilling fluid returns which show such changes.

Further objectives and advantages of the present invention when applied both in a continuous manner and in batch operations will become apparent from the following detailed description taken in conjunction with accompanying drawings which form an integral part of the present specification.

In the drawings:

FIG. 1 is a schematic illustration of apparatus for analyzing formation samples for a point-by-point determination of gasoline fraction hydrocarbons therein;

FIG. 2 is a schematic representation of a preferred form of apparatus for extracting and analyzing a sample of the drilling fluid returns from a well bore during drilling, as applied to a conventional rotary drilling system;

FIG. 3 is an alternative form of the sample-extracting and analysis system, useful in analyzing the drilling fluid for the presence of low molecular weight hydrocarbons with an infrared spectrometer;

FIG. 4 is a graph of the relative quantities of aromatic hydrocarbons detected in drilling fluid returns in a well bore penetrating both commercially valuable oil and remnant petroleum deposits;

FIG. 5 is a block diagram of a system using gas liquid partition chromatography to analyze a sample of a formation;

FIG. 6 is a schematic illustration of details of the apparatus employed in the system illustrated in FIG. 5;

FIGS. 7 and 8 illustrate records of chromatographic analyses of side wall samples.

Referring now to the drawings, and particularly to FIG. 1, there is illustrated apparatus for batch analysis of drill fluid returns or other formation samples for gasoline fraction hydrocarbons. In this figure, a distillation vessel 11 contains the sample, such as drilling fluid returns, water (when required to reduce viscosity), and an organic solvent, such as iso-octane or toluene which acts as a volatile carrier for the gasoline fraction hydrocarbons. This vessel is heated by heating mantle 12 and by steam passing into the vessel from line 13. This steam is generated in vessel 4 by heating Water in said vessel by means of mantle 5. The vapors initially arising from the mixture in vessel 11 may be condensed by reflux condenser 16 and return to the vessel as liquid. If this refluxing is continued until the entire sample is very fluid and highly agitated by the incoming steam, then I have found that more eflicient extraction can be accomplished in shorter time than by other methods. However, with some samples I have found that an adequate separation of the gasoline fraction hydrocarbons from the sample and concentration thereof in the distillate can be obtained with little or no refluxing in this stage of the distillation process. I have found, also, that adequate separation and concentration of the gasoline fraction hydrocarbons in the distillate can be obtained without refluxing but by adding the carrier solvent in consecutive portions to the vessel 11 as the distillation of the sample progresses.

When the reflux condenser 16 is used in the distillation apparatus, after suflicient reflux the cooling water supplying this condenser is shut off at valve 17, and valve 18 is opened; this allows condenser 16 to drain. Reflux condenser 16 is then rapidly heated by the rising vapors, in the absence of cooling Water, and the vapors from vessel ll pass directly into another condenser 19 where they are condensed to the liquid state and run into receiver 2d. Receiver 2% may be cooled by ice 21 in vessel 22 in order to preserve efficiently the volatile materials separated from the drilling returns.

Application of the method of the present invention to a conventional rotary drilling rig is illustrated in FIG. 2. As there indicated, the lower end of a drill derrick 41, and specifically the mud return line 44, lying below the rotary table 42, are shown partially in section. In this system of drilling, drilling fluid enters the drill string through kelly bar section 43 and is pumped down the drill string running to the bottom of the well bore. As drilling proceeds, the drill bit is lubricated and cooled by the drilling fluid, and the flushed fluids and rock chips are flushed upward through casing 44. The drilling fluid also maintains a hydrostatic head in the borehole that normally exceeds any pressure encountered along the borehole. The drill pipe passes through a blowout preventer, indicated schematically as 45, which acts as a safety device if pressure in the well bore exceeds the hydrostatic head. The mud from the well bore returns to sump 4? through a return line 47 and a chip-removing screen, better known as a shale shaker," 48.

The drilling fluid used in such rotary drilling method may be a mixture containing barytes and clay or other weighting and thickening agents in water, called waterbase mud, or it may have an oil base or even be based on a combination of oil and water, better known as an emulsion mud. In accordance with the present invention, wherein it is desired to analyze the returned drilling fluid for those gasoline fraction hydrocarbons which are most indicative of commercially valuable oil, l have found that such light hydrocarbons contained in sedimentary rock can best be separated from the drilling fluid, whether oil, water, or emulsion based, by the addition of heat to generate steam. In the present embodiment, such heat is supplied by flowing steam into the mud sample through line 53, which enters a heating zone, represented in FIG. 2 by heat exchanger 52. Desirably, a small amount of oxygen gas is admixed with the steam prior to injection into heat exchanger 52 for a purpose to be elaborated hereinafter.

As indicated, at least a portion of the drilling fluid is bypassed out of the normal return line :7 through enclosed stream divider 5i and then passes downward through the heating zone provided by heat exchanger 52 and along a tortuous path defined therein by haflles 54. As the mud stream flows down through heat exchanger 52, is is permitted to contact steam introduced through tube 53. As has been explained more fully heretofore, the steam performs the dual functions of vigorously agitating the drilling fluid as it flows across baffles '4 and of adding sufiicient heat to cause water vapor and the hydrocarbons volatile a 100 C. and slightly above to be driven off together with only a small amount of water va oor being added to the sample by the steam entering through line 53. The stripped drilling fluid is then returned through 5?,- to mud pit The vapor of water and the aforementioned volatile hydrocarbons will rise through vapor line 56 and enter condenser 57, wherein the vapors are permitted to condense as a liquid sarnole. Deslably, but not necessarily, noncondensed gaseous materials, such as light hydrocarbons in the C to C range, air, and excess oxygen, are permitted to escape through bypass 59. The remainder of the liquid sample now saturated with dissolved oxygen gas, first admitted through line 53 and later dissolved the liquid sample on cooling in condenser 57, is then exposed to radiant energy to permit analysis of at least one component thereof.

In the form of apparatus shown in FIG. 2, the liquid sample flows through an irradiation tubing 61 that passes through and in close proximity to a strong source of gamma rays. This source, such as cobalt 60, may be formed in the share of a pipe as that surrounds the tubing 61. Radiation source as is, of course, housed within suitable shielding as which surrounds pipe =52. Shielding material, such as lead, tungsten, or other dense material, is, of course, suitable for absorbing emitted gamma rays not entering the sample.

As mentioned heretofore, high-energy gamma rays react with water to form free hydroxyl radicals. These very reactive free radicals in turn react with dissolved benzene and other aromatic hydrocarbons in the presence of dissolved oxygen to form phenol and phenol derivatives. in the present instance the conversion of such benzene to phenol makes the iluid sample more susceptible to automatic, and accurate, analysis for the presence of benzene in the original sample.

In this analysis a color additive such as a mixture of phosphomolybdic and phosphotungstic acids with an excess of sodium carbonate is supplied from tank ss through valve 67 in a manner so that it ecoines intimat ly mixed with the irradiated sample leaving tube 61. The sample is then introduced into a colorimeter 2'? where the presence or absence of the phenol and phenol derivatives derived from benzene and other aromatic hydrocarbons is determined by the i r sence of the characteristic blue color and is then recorded by galvanometer 29 on chart 31, which is driven in accordance with a time base by synchronous motor 32.

In relating an indicated incerase in benzene in the sample liquid to the depth of the drill bit, chart 31 may be correlated with the drihers log. If desired, of course, chart 31 may be driven directly by a depth indicator connected to the depth indicator for the drilling string in the well bore. These and other methods of synchronizing a recorded quantity with tie depth of drilling are well known in the well logging art.

In accordance with another method of carrying out the press. t invention, there is illustrated in FIG. 3 an alternative analysis system. As there shown, the heating zone is re oresented again by heat exchanger $2. Drilling fluid returns containing hydrocarbons whose presence are to be sampled enter heat exchanger 52 through line 51, and the stripped drilling fluid leaves by line 58. While steam is indicated as being added through line 53, for the same purpose as explained in arrangement of FIG. 2, there is additionally provided for the heat exchanger 52 an insul .g cover 71 having hnbedded therein heater coils, represented by electrical resistance Wire 73, supplied by a suitable power 5 ec through lines 75. purpose of this arrangement is to insure that the temperature of the drilling fluid returns is maintained suliiciently high to assure distillation of essentially all the gasoline fraction hydrocarbons over into the vapor condenser section 57 through line 56.

As further distinguished from the previous embodiment, there is provided a method of adding to the sample fluid a carrier liquid which is inert in the subsequent analysis, which distills readily at the temperature employed, which is capable of being dried of all traces of water, and which dissolves the gasoline hydrocarbons selected for analysis. The carrier liquid permits the dried liquid sample to pass through a water-soluble crystal, such as sodium chloride, during the infrared analysis of the hydrocarbon components. in the present instance this is accomplished by the addition of iso-octane which has a normal boiling temperature of 9 C. at atmospheric pressure. so-octane is introduced through line 77 so that it may be heated and join the stream of vapors, as they are driven off of the drilling fluid passing through and over baffies 54.

The mixture of vapors of water, gasoline fraction bydrocarbons, and iso-octane passes through flow line 56 to condenser 57, wherein the vapors are condensed to a liquid form. In condenser 57 will be formed two liquid phases, one Water and the other iso-octane. The gasoline fraction hydrocarbons pass essentially entirely into the organic liquid phase. This mixture of organic (i.e., hydrocarbon phase) and water phase is passed to waterhydrocarbon separator 83. In separator 81, there is provided a settling tank 83 wherein the Water and hydrocarbon phases separate from each other by gravity. The hydrocarbon phase, being lighter than Water, floats on the surface. At this point in the flow system, it may be desirable to provide an outlet vent 8d for the escape of permanent gases, such as hydrocarbons ranging from one to four carbon atoms, and air from the system.

The actual separation may be accomplished entirely by gravity or may be improved by preferential hydrocarbon-, and water-wet filtering elements indicated as 85 and 87, respectively. Filter element 87, for example, is a ceramic filter that is preferentially Water-Wet and contains relatively small openings so that water preferentially passes through the filter even in the presence of either a continuous hydrocarbon phase or a discontinuous phase of small droplets of hydrocarbon. Similarly, the filter element 25 is preferentially hydrocarbon-Wet, so that hydrocarbon compounds will pass therethrough. One material suitable for such preferential hydrocarbon-wet filters is porous carbon.

Following mechanical separation of water in the hydrocarbonwater separator 81, the small traces of water actually dissolved in the iso-octane must be removed before passing the sample into the infrared cells with their Water-soluble sodium chloride Windows. For this and other purposes, purifying tubes 83A, 38B, and 38C are provided in flow line 88 which connects the outlet of water separator 81 with infrared spectrometer 79. Purifying tube 88A contains a chemical water-removing agent which may be anhydrous calcium sulfate such as the commercial preparation marketed under the trade name Drierite. It will be found convenient to make drying tube 83A of glass and to fill this tube with the so-called indicator Drierite which indicates that it has absorbed all the water of which it is capable by changing from a blue to a pink color and thus signaling the need for replacement. Tube 83 8 contains a carbon dioxide absorbant such as the aforementioned Asc rite to eliminate the large carbon dioxide peak at 15.15 microns which would interfcre with the detection of traces of benzene.

I have also found that after passing the gasoline fraction hydrocarbons containing iso-octane through the aforementoned purifying tubes, small particles of the purifying agents tend to be suspended in the solvent. In particular, small particles of the order of 10 to 20 microns in diameter cause interference with the infrared spectrum in the 12.5 to 15 micron range, and must therefore be removed. I have found that simple settling is sufiicient to remove such interference and therefore have included tube 88S,

3 which can be either a small settling tank or a tube filled with filtering agent such as fine glass fibers known as glass wool.

Following separation of iso-octane and the hydrocarbons dissolved therein from all traces of Water and of carbon dioxide in separator 81 and purifiers 88A, B, and C, the sample is passed into an infrared spectrometer '79. In the present instance, the spectrometer is indicated schematically as including a pair of sample cells 89 and 91 with sodium chloride crystal windows. Such cells are standard for use in the 12.5 to micron region. We have found the aforementioned cell thickness of 0.2 inch to be appropriate when extraction procedure is adjusted so that the gasoline fraction hydrocarbons contained in 50 volumes of drilling fluid are concentrated in one volume of iso-octane by the steam distillation and extraction procedures. One of these cells, 91, contains a sample of the pure solvent (iso-octane in the aforementioned discussion). Fluid samples from the separator 81 pass through the sample cell 89. In this way, the optical absorbance of the sample and of the standard liquids may be continuously compared by infrared spectrometric analysis.

As is well known in the art, spectrometer 79 includes an infrared source 93 supplied by battery 95 so that it emits substantially white infrared radiation. Said infrared radiation is then passed through slits 97A and prism assembly 97 and a particular wave length in the infrared region is selected and passed as a beam to mirror system 99. Mirror system 99 splits this infrared beam into two equal parts which are passed respectively through standard sample 91 and sample cell 8?. The light passing through the lenses is then concentrated on the thermocouple junctions, indicated respectively as ltlS and 1W. The unbalance in EMF generated by thermocouples H35 and 107 is then measured by galvanometer 139 and recorded on chart lll, driven by synchronous motor 113. The increase or decrease of a particular constituent hydrocarbon in the fluid sample extracted from the drilling fluid is then recorded in accordance with a standard time base, or the depth of the well bore.

Infrared analysis may be accomplished in several other ways. An infrared spectrometer, adjustable as to wave length, such as described herein, may be employed. Said spectrometer can be made to scan the entire spectrum in the region of 12.5 to 15 microns by attaching an automatic drive mechanism to prism $7 in such a manner that the energy transmitted through slits 97A and mirrors 99 to the sample cells is caused to change at a uniform rate as a function of time. Conversely, the automatic drive can be adjusted to skip from absorption peak to peak quickly and then pause at each peak leng enough for the sensing mechanism to come to equilibrium and record a true value. The Wavelengths selected for such peaks are best selected from those detailed in the earlier part of this specification as being characteristic of arcmatic hydrocarbons of interest.

Another alternative mechanism is to use several sample cells 89 connected in series so that the fluid sample flows through each cell in turn. Each cell is irradiated with infrared radiation of a dilierent wavelength, said wavelength being characteristic of a specific aromatic hydrocarbon, the radiation transmitted by each cell being received by a separate detector and recorded as a separate trace upon a chart; thus, a continuous record is obtained of each constituent or interest.

Another very practical variation of this method may utilize a so-called nondispersive infrared instrument. In such an instrument, the prism and slit mechanisms 7 and 97A are replaced by a filtering system. Such filters may be of the optical interference type, but usually consist of liquid materials selected to absorb all the infrared radiation except that falling in a narrow wavelength band about the wavelength at which the material of interest absorbs. If such a filter is used instead of the prism system, the apparatus becomes very much less expensive and frequently more sensitive to a specific component. Of course, the disadvantage of this system is the loss of ease of adjustment of the wavelength, but this is no disadvantage in my usage where specific compounds with known specific absorption wavelengths are sought.

1* is apparent that many possible variations in this instrumentation will occur to those skilled in the instruent arts. Such variations are numerous and do not in any way comprise a variation of this invention but merely a variation in its execution. Such analysis may either be made simultaneously or in succession, as desired. The present arrangement indicates the system to be continuous in operation. It will also be apparent that the particular method of analysis will depend upon the need and desirability for such continuous measurement of the drilling fluid. Additionally, it will be understood that batch samples can be taken at discrete itnervals during the drilling of a well and then individually analyzed by the present method and that samples of subterranean formations obtained by other means than from the return drilling fluid can likewise be analyzed by the infrared method. Such analysis will, of course, be conducted at intervals required by the particular Well being drilled for exploration of potential oil accumulations.

Other methods of analysis may be applied to detection of selected gasoline fraction hydrocarbons in formation samples, including drilling fluid returns, the solid drill cuttin s, the circulating fluid, or admixtures thereof, in sidewall samples, and in cores. In particular, when it is desired to analyze for selected cycloparatlins, such as cyclopentane, cyclohexane and methylcyclohexane or acyclic paraifins, a suitable mass spectrometer may be used.

Analysis of the distillate from formation samples for cycloparaifins and paraffins of the preferred five to nine carbon atoms may also be obtained by the well-known technique of gas-li id partition chromatography (see, for example, I). H. Lichtenfels, S. A. Fleck, and F. H. Burrow, Analytical Chemistry, October 1955, vol. 27, No. It), pp. l5l0-l513). This is one of the preferred techniques for the purpose of this invention and may be used on a batch basis, or by employing a multiple bank of gas-liquid partition chromatography instruments, semicontinuous operation may be obtained.

PEG. 5 illustrates in block diagram form an arrangement of apparatus by which a gas liquid partition chromatography analysis may be made. As there shown, the apparatus includes distillation means 11A and appurtenances, separating device 121, and a chromatography analysis means including carrier gas source 131, sample insertion means 12%, partitioning column 136, detector 11 and recorder 14$.

The operation of this form of apparatus is shown in schematic detail in FIG. 6 as applied to the analysis of drilling fluid returns. In this illustration, the drilling fiuid returning from the well bore to the mud pits flows through the mud flow line shown in cross section at 47. Samples of this mud stream are allowed to flow into distillation vessel 11A through pipe 51A by opening valve 2 for suitable periods of time. Valve 1% may conveniently be a fixed volume-measuring valve.

After the mud sample is placed in distillation vessel 11A, a volatile solvent carrier for the gasoline fraction hydrocarbons is added to the sample. The Volatile solvent carrier 1% is contained in vessel 114 which is in communication with distillation vessel 11A through metering valve 11.5 and tube 116. The addition of the volatile carrier to the contents of the distillation vessel may be made in one step prior to or during the initial stages of distillation, or may be spread out either continu usly or in small increments during most of the duration of the distillation process. It is preferred, however, that approximately the last quarter of the distillation be l made without the further addition of volatile carrier to the contents of the distillation vessel.

The gasoline fraction hydrocarbons contained in the mud sample and in the presence of the volatile solvent carrier are then steam-distilled from the distillation vessel llA by the addition of steam to the latter through pipe 13A. Steam 8 may be generated in vessel 14A by the application of heat by heater 15A to water 96. Heater 15A conveniently is an electrical heater deriving its power from battery 94. The flow of steam to the distillation vesel is controlled by valve ltlll.

The first steam passing into distillation vessel 11A serves to heat the mud sample to substantially 1%" C. At this point, substantial volumes of vapor begin to pass from distillation vessel 11A through overhead conduit 117 into condenser 11%. In condenser 113, these vapors are condensed by the action of cooling water 119. Two phases condense in condenser 11%; one phase is essentially pure water, and the other a mixture of the gasoline fraction hydrocarbon derived from the drilling iluid sample and the carrier fluid 1% added prior to or during distillation. These two phases pass dropwise (E29) into separator 121.

In separator 1211, the two phases formed in condenser 1.13 are separated by taking advantage of the difference in their specific gravities. Both phases pass initially through funnel 122 but quickly separate into a water phase 124 and a hydrocarbon phase 123. The volume of separator 1.21 below the wier 126 is chosen such that the volume of water 124 required to fill this part or" the separator is adequate to insure that a major portion of the gasoline fraction hydrocarbons of the mud sample will have been distilled into the separator by the time the rising water level causes the hydrocarbon phase 123 to flow across wier 126.

From wier 126 the hydrocarbon phase flows into the cold trap 154}. This cold trap is convenientl cooled by ice 152 in container 154 within which the cold trap 150 is immersed. By maintaining the cold trap at 0 C., the recovery in the distillate of pentane from the mud sample will be substantially complete. A small amount 156 of the carrier solvent 1% used in the distillation process may be placed in cold trap 1543, sufiicient to immerse the open end of tube 153 through which the cold trap communicates with the separator 121 Thus, if a large amount of gas is evolved during the heating of the drilling mud sample in distillation vessel 11A, which gas may result from air or C through C hydrocarbons entrained in the mud sample, the cold carrier solvent 156 strips any gasoline fraction hydrocarbons, and in particular pentane, from this gas as it bubbles out of the end of tube 158 and through the solvent 156. The stripped gas escapes from the cold trap through vent 160.

If it is desired to use this apparatus to extend the range or" investigation into that of light gases, to include in one apparatus the facility for performing a conventional gas analysis of drilling fluid as well as the analysis for gasoline fraction hydrocarbons in accordance with my invention, then cold trap 151? may be cooled to a lower temperature than that accomplished by the ice bath mentioned heretofore by using solid carbon dioxide or so-called Dry Ice in place of the water ice 152 in container 154. In this connection, the choice of toluene as a solvent carrier fluid is particularly convenient, since its melting point is 95 C., considerably below the temperature readily obtainable with Dry Ice.

When distillation is completed, sufiicient water will have been condensed into separator 121 to cause the surface of the water to closely approach the level of the wier 126, thus causing substantially all of the solvent carrier, and the gasoline fraction hydrocarbons dissolved therein, to ilow over the wier and into the cold trap 15%. This concentrate is added to and mixes with the portion 155 of carrier solvent which was placed in the cold trap prior to starting the distillation process, and any gasoline fraction 1'6 hydrocarbons which were stripped from the gases evolved during distillation, as explained heretofore, become part of the concentrate to be analyzed.

The contents of the cold trap can be withdrawn from it through a tube 162 and check valve 127 into a syringe 123 by partially withdrawing the plunger of the latter. The check valve 127 prevents a reverse flow of the concentrate through the tube 162 when the plunger of the syringe is depressed.

The syringe 128 communicates through a check valve 164 ard c lary tube 12-9 with a flash vaporizer 130. The fla l1 vaporizer can be connected through a two-way valve 156, operated by valve control 16?, either to a purge line 153 or L0 the chromatograph column 136 through carrier gas line 17%. The lash vaporizer 13% may conveniently consist of an electrical resistance heating coil an appropriate battery to energize it.

The valves l'c d on the distillation vessel 11A, on separator 121, and 172 on cold trap 15% are provided to empty the respective vessels of their liquid contents after the analysis of each sample has been run and before a new sample is taken into the system. Preferably, also, as mentioned heretofore, the capillary tube 129 and flash vaporizer 139 are purged by a portion of the concentrate of each new sample to remove possible contamination or residue or" previous samples prior to making the chromatographic analysis. To this end, the two-way valve 166 and purge line 168 are provided to permit a portion of concentrate drawn into the syringe 128 to be forced through the capillary tube and flash vaporizer, preferably while the latter is in operation, and thence purged to the atmosphere without entering the chromatograph column. When purging is complete, the two-way valve 166 is operated to direct the contents of the flash vaporizer into the chromatograph column so that the analysis of the distillate or concentrate may proceed. Check valve 164 is provided to prevent reverse how or the concentrate from the capillary tube 12) into the syringe 128 while a fresh charge of the concentrate is being drawn into the syringe from the cold trap 15%.

The gas liquid partition chromatograph apparatus comprises two int rrelated but essentially independent sys terns: the carrier gas and sample system, and an electrical sensing system. It is convenient to first describe each of these systems independently and then describe the consequences of injecting the sample to be analyzed into the chromatograph assembly.

The gas system begins with a cylinder 131 of compressed carrier gas. This carrier gas is usually hydrogen, helium, or air, but may be any gas appropriately chosen to be used with the detector system. The pressure in cylinder 131 is reduced to an appropriate working pressure by regulator 132. The flow rate of the carrier gas is then controlled by the flow regulator 133. The constant flow of carrier gas leaving regulator 133 passes sequentially through the following parts of the chromatograph: reference detector 134, chromatograph column 136, bypass valve 138, detector 135, and vent 142. The electrical detection system consists or a bridge circuit (described hereinafter), an amplifier 14-4 and a recorder 145. The bridge circuit consists of battery 1.4-1, reference arms 13$ and 14%, reference sensing element 134, and detector sensing element 135. The sensing elements 134 and 135 may take many forms. In gas chromatographs utilizing hy rogen or b lium as a carrier gas, the sensing elements are characteristicaly thermal-conductivity detectors. When the carrier gas is air, the sensing elements may be a catalytic combustion detector.

As mentioned above, when the plunger of syringe 128 is depressed, a portion of the concentrate of the liquid carrier solvent, and the gasoline fraction hydrocarbons contained therein is forced through the capillary tube 129 and into flash vaporizer 13 The temperature of the dash vaporizer 138 is maintained at a sufficiently high value to essentially instantaneously convert into vapor the stream of mixed hydrocarbonsentering into it. This vapor is carried by the stream of helium gas directly into the column 136. In column 136, the various components of this hydrocarbon sample interact with the stationary liquid which constitutes the column packing 137. The separation of the hydrocarbons in the sample is brought about by interaction with the stationary liquid packing 137 in a manner according to the principles expounded in the above-named reference publications on gas chromatography.

The effluent from column 1336 consists of carrier gas intermittently contaminated with a single separated cornponent of the mixed hydrocarbon sample injected into the apparatus. As each of these components pass through detector 135, they bring about a change in the physical state of this detector resulting in an unbalance of the bridge previously described. The unbalanced signal from this bridge is fed into amplifier 14 and recorder 145 and causes pen 1 .6 to trace a curve 147, the amplitudes of individual excursions in which curve correspond to the amount of various components present in the original mud sample. If the chart of recorder 145 is moving in synchronism with the flow of carrier gas in the apparatus, then the position of each peak on the chart can be. correlated with the specific hydrocarbon causing the peak according to the principles well known in this field.

A difficulty might arise with this system when applied to the analysis of formation samples, such as those obtaineu from drilling fluid, in the following manner. The bulk of hydrocarbon sample 123 is carrier liquid 106. The gasoline fraction hydrocarbons of interest are present as mere traces in this carrier liquid. Consequently, when the separated vapor sample corresponding to the carrier liquid passes through detector 135, it may cause a severe unbalance in this detector, which has been designed and adjusted to detect the trace components dissolved in the cmrier liquid. To prevent this difficulty, value 133, operated by value control 148, is provided, by which means the slug of vapor and carrier gas corresponding to carrier liquid the can be diverted from the apparatus prior to reaching detector 135 and hence prevent extreme unbalance of the bridge circuit and subsequent insensitivity.

It will be understood that the present invention generally comprehends obtaining an evaporate from samples of a subterranean formation, which sample may be in the form of a core, a side wall sample, drilling fluid returns, or aliquot portions thereof, either continuously or from successive samples, and analyzing the evaporate for one or more gasoline fraction hydrocarbons, either individually or collectively. The identification of said hydrocarbons, along with changes in their amount and relative abundance from sample to sample, or progressively from continuous samples, provides a method for indicating that a given horizon in formations penetrated by a drill bit either conta'ms or is adjacent to an oil accumulation. When the indications based upon the gasoline fraction hydrocarbons signify oil of commercial value, the horizon which was sampled is examined further by dynamic fluid flow testing means, well known in the oil industry, to determine its ability to produce oil in commercially valuable quantities. As previously mentioned, under some conditions side wall samples or cores are conveniently and advantageously used in place of drilling fluid samples. Although it would be desirable to devise a means for totally encasing a side wall sample or core from the moment of its removal from the formation until its analysis, it is at present more practical to bring the sample to the surface and place it in a tightly closed jar. I have found it beneficial, when hanling such side wall samples or cores, to cool the jars and samples to Dry Ice temperature to prevent the escape from them of the more volatile hydrocarbon components. When the sam les are thoroughly cooled, they may be removed from the jar and transferred to a similarly cooled pestle and mortar and crushed without undue loss of C through C hydrocarbons.

The crushed sample is transferred to the distillation vessel, water is added, and the distillation proceeds in the manner explained heretofore. Alternatively, the distillation vessel itself may be modified to include an externally operated sample-crushing device. With this modification, the entire side wall sample, including the glass jar, may be placed in the distillation vessel without cooling. The sample-crushing device is then operated to crush both the jar and the sample. Distillation then proceeds in the manner explained.

To further explain the nature of my invention, there is shown in FIG. 4 a portion of a drilling fluid log that was obtained by examination of drilling fluid returns from a well drilled in Cymric Field, in the San Joaquin Valley, Kern County, California.

In FIG. 4, the vertical scale corresponds to the depth of the drill bit beneath the surface of the ground, measured in feet, at the time the several samples were taken. The horizontal scales refer to the concentration of three selected gasoline fraction hydrocarbons in terms of their concentration in the drilling fluid returns in parts of hydrocarbon by volume per million volumes of drilling fluid. The three hydrocarbons selected are benzene (3.1. 80.1 C.), toluene (B.P. 110.6 C.), and meta-xylene (B.P. 139.1" C.).

The concentration of the above-mentioned components in each sample was obtained by the method illustrated in FIG. 1. In this method of batch steam distillau'on, 500 milliliters of the drilling fluid returns were placed in vessel 11, and to this was added 10 milliliters of isooctane. Distillation was carried out until the 10 milliliters of isooctane added was recovered and an additional 40 milliliters of water distilled over. Under these conditions, percent of the benzene was removed from the sample and aproxirna-tely 70 percent of the toluene and 60% of the meta-xylene. The iso-octane was mechanically freed of water, dried with Drierite drying agent, the carbon dioxide removed with Ascarite treating agent, and the powdered residue from these purifying agents allowed to settle as in the system shown in FIG. 3. The sample was then transferred to a sodium chloride windowed cell of 0.2 inch thickness and -a comparative infrared spectrum run against pure iso-octane in a Perkin-Elmer Model 21 instrument. Determination of the concentration was made by comparison with pure standards.

Referring again to FIG. 4, it can be seen that in the interval between the foot of the surface conductor pipe (i.e., the beginning of sampling) and 700 feet, a relatively large ratio of meta-xylene and toluene to benzene was encountered, compared to this ratio when drilling in an oil sand. Such an indication is indicative of a high average molecular weight, high viscosity, hydrocarbon ac cumulation, such as a tar deposit or an artificially or naturally depleted oil sand. Such is indeed the case, for this region is well known to contain a noncommercial, viscouse, residual oil accumulation.

From 700 feet to 2,000 feet, the amount of toluene and xylene decreases as these materials gradually evaporate from the shale shakers and the mud pits. Between 2,000 feet and 2,930 feet, no new hydrocarbons are added to the mud, and a minimum indication is obtained. Below 2,930 feet, a sudden increase in all components begins and continues to 3,330 feet. Most of this interval is known to be shale except for the interval 3,270 to 3,320, which is an oil-productive sand in this area. The increase in concentration of benzene, toluene, and meta-xylene is a spectacular warning of the approach to the oil horizon. These indicaitons in the shale can arise from oil in very thin sand lenses in the shale.

A formation test was made between 3,270 and 3,330 feet, followed by two electric logs run between 3,330 and 3,420 feet. These operations require conditioning of the hole, which involves a large amount of circulation of drilling fluid but little drilling; as a consequence, the volatile benzene rapidly evaporates from the drilling fluid 19 on the shale shakers and in the mud pits. Toluene and xylene, being less volatile, evaporate less rapidly. From this point, a new base line is established.

Again, from 3,420 to 3,600 a gradual but large increase in'concentration of all components is observed, followed by a plateau from 3,609 to 3,700. The well is completed for commercial oil production in the later interval. The interval from 3,420 to 3,600 is again normally designated as a shale.

The foregoing description of an application of my invention makes clear many of its virtues. There is a clear indication of commercial oil. Low molecular weight gases in gas accumulations of one kind or another give no indication, of course, as they do not contain appreciable gasoline fraction hydrocarbons. A depleted residual oil sand is distinguished from a commercial oil show by a smaller magnitude indication of all three components and a larger ratio of Xylene and toluene to benzene than for commercial oil. The approach to commercial oil is indicated more than 100 feet prior to the penetration of the oil sand by the drill bi-tvery valuable information, indeed, as this permits coring or other careful investigation of the interesting zone while the bit is drilling at that depth.

FIGS. 7 and 8 illustrate chromatograms obtained from the anaysis of two side wall samples from a well at Huntington Beach, California. FIG. 7 represents the analysis of a side wall sample taken from a gas-productive sand at a depth of 1860 feet in the well bore, and FIG. 8 represents the analysis of a side wall sample taken from an oilproductive sand at a depth of 2196 feet in the same well bore.

A comparison of these chromatograrns reveals a pronounced dilierence in the hydrocarbon content of the two samples. This difference can be used to distinguish oil sands from gas sands. In chromatogram A, illustrated in FlG. 7, the low-boiling constituents represented by the pentanes and the hexanes, which appear in the first part of the record, are essentially as abundant as the heptanes and the octanes which appear later in the record. analysis indicates a sand of high gas content. In chromatogram B, illustrated in PEG. 8, it is evident that the lower boiling constituents are much less abundant than the high-boiling constituents, thus indicating a petroleum accumulation consisting primarily of liquid oil. As mentoned previously, specific paralhnic or cycloparaflinic com pounds also are diagnositic for this purpose.

Other differences areapparent between these chromato grams which are more readily correlated with the different geological environment from which these two samples were obtained than with the difference in the relative amount of gaseous hydrocarbons in the horizon. For instance, chromatogram'A is characterized by a relatively large abundance of isoparafiin hydrocarbons with respect to the corresponding straight chain or normal paraifins. In chromatogram B, the isoand normal components are roughly equivalent in abundance. Furthermore, chromatogram B has significantly more methylcyclopentane than chromatogram A. Differences such as these are useful in correlating horizons between adjacent wells.

Accordingly, it will be understood that the present invention generally comprehends the identification in the sample of a subterranean formation or horizon penetrated by a well bore, which sample may he obtained from known or determinable elevations in the well bore after it has been drilled, or from cores extracted while the well bore is being drilled, or from the drilling fluid, including whole drilling fluid returns or the separate components thereof of hydrocarbons that occur in or are characteristic of the gasoline fraction of commercial oil. Such identification of hydrocarbons permits a determination of formations or-horizons which are potentially coinmercially productive, and also a determination, while '7 20 the well here is being drilled, of the proximity of such formations or horizons.

I claim:

1. A method of determining the presence of commercially valuable oil in the course of drilling a well bore which comprises circulating drilling fluid in the well bore, whereby said drilling fluid contacts the earth formation at the bottom of the well bore and is returned to the wellhead, taking a series of samples of the drilling fluid returns, subjecting each of said samples to evaporative conditions to obtain gasoline fraction hydrocarbons from said sample, adding a volatile carrier during said evaporation to aid separation of said fractions, collecting the evaporates including said carrier as .a concentrate, analyzing said concentrate to determine t e amount of at least one selected gasoline fraction hydrocarbon whereby changes in the selected hydrocarbon content in said series of samples of drilling fluid returns may be correlated fill}. the horizon of the formation at the bottom of the hole in contact with the drilling fluid samples indicating a change.

2. The process of claim 1 where-in said concentrate is analyzed for at least an aromatic hydrocarbon of 6 to 8 carbon atoms.

3. The process of claim 1 wherein said concentrate is analyzed for at least a cycloparafiin hydrocarbon having 6 to 7 carbon atoms.

4. The process of claim 1 wherein said evaporation of said gasoline fraction hydrocarbons and said volatile carrier is carried out with the aid of a gas which promotes the volatilization of said selected gasoline fraction hydrocarbon from said drilling fluid returns, and said gas is excluded from said concentrate prior to analysis for said at least one selected gasoline fraction hydrocarbon.

5. A method of determining the presence of commercially valuable oil while drilling at one or more horizons in a well bore from the change in abundance of at least one gasoline fraction hydrocarbon in the drilling fluid returns from said well bore, which method comprises the steps of subjecting at least a part of the drilling fluids returns to evaporation in the presence of a volatile carrier added to aid separation of gasoline fraction hydrocarbons from said fluid, collecting the evaporate including said carrier as a concentrate, analyzing said concentrate to determine the amount of at least one selected gasoline fraction hydrocarbon therein whereby changes in the selected hydrocarbon content in said drilling fluid returns may be correlated with the geological horizon at the bottom of the well bore contacted by said drilling fluid returns.

6. The process of claim 5 wherein said concentrate is analyzed to determine the relative amounts of a plurality of gasoline fraction hydrocarbons of at least 5 carbon atoms and boiling in the range of 40 C. to 180 C.

7. The process of claim 5 wherein said concentrate is exposed to infrared radiation and the amounts of aromatic hydrocarbons is determined by the characteristic absorp-' tion peaks in the transmitted radiation.

8. The process of claim 5 wherein said concentrate is analyzed by gas-liquid partition chromatography for at least one gasoline fraction hydrocarbon selected from cycloparalilns and paraflins.

9. A method for determining the presence of commercially valuable oil in the course of drilling a well bore which comprises circulating drilling fluid in a well bore, whereby said drilling fluid contacts the earth formation at the bottom of the well bore to entrain cuttings and fluids drilled up in forming said well bore and then returns to the wellhead at the earths surface, withdrawing a sample of the drilling fluid returns, addin an organic solvent carrier fluid to said sample to aid separation of gasoline fraction hydrocarbons therefrom during heating, evaporating from said sample both said organic solventcarrier fluid and said gasoline fraction hydrocarbons at a temperature of less than about C. at atmospheric pressure, separating, collecting, and condensing the'evap-i crates to form a concentrate of said carrier fluid having said gasoline fraction hydrocarbons dissolved therein, and analyzing said concentrate to determine the amount of at least one selected gasoline fraction hydrocarbon whereby changes in the selected hydrocarbon content of said drilling fluid returns may be correlated with the horizon at the bottom of the well bore in contact with the drilling fluid returns.

10. The method of determining the presence of accumulations of commercially valuable oil while drilling a well bore, which comprises circulating drilling fluid in the well bore, whereby said drilling fluid contacts the earth formation at the bottom of the well bore to entrain cuttings and fluids drilled up in forming said Well bore and then is returned to the wellhead, withdrawing a series of samples of the drilling fluid returns at predetermined depth intervals in the drilling of said well bore, adding an organic solvent carrier fluid having a boiling point of less than 100 C. at atmospheric pressure to each of said successive samples, subjecting each of said samples to evaporative conditions to separate therefrom by volatilizetion at least a plurality of aromatic hydrocarbons of 6 to 8 carbon atoms, condensing the distillate from each of said successive samples to form a concentrate of sm'd carrier and said aromatic hydrocarbons, and analyzing said concentrate from each of said samples to determine the relative amounts of said aromatic hydrocarbons whereby the ratios of said amounts of a selected pair of said aromatic hydrocarbons may be correlated with the horizon of the formation in contact with each drilling finid sample to indicate a change in the relative quantity of commercially valuable oil in said horizon.

11. A method of determining the presence of commercially valuable oil in subterranean formations penetrated by a well bore which comprises obtaining samples of subterranean formations from vertically spaced-apart locations at predetermined dep is in a well bore, subjecting each of said samples separately to evaporative conditions to obtain gasoline fraction hydrocarbons from said sample, adding a volatile carrier during said evaporation to aid separation of said fractions, collecting from each sample separately the evaporates including said carrier as a concentrate, analyzing said concentrate to determine the amount of at least one selected gasoline fraction hydrocarbon in each said sample, and comparing the change between said samples of the amounts of said at least one gasoline fraction hydrocarbon in correlation With the depth of said borehole at which the respective said samples were talcen as an indication of the presence and location of commercially valuable oils in the subterranean formations penetrated by said borehole.

12. A method in accordance with claim 11 wherein said samples are obtained from formations exposed at the side Wall of said borehole after said borehole has been drilled to a depth exceeding that of said formations.

13. A method in accordance with claim 11 wherein said samples are obtained at successively greater depths in said borehole at the location of a drill bit at each of said depths respectively as said borehole is being drilled.

14. A method in accordance with claim 11 wherein said volatile carrier is iso-octane and said concentrate is analyzed by infrared spectroscopy.

15. A method in accordance with claim 11 wherein said volatile carrier is toluene and said concentrate is analyzed by gas liquid partition chromatography.

16. A method of determining the presence of commercia-lly valuable oil in a subterranean formation penetrated by a well bore which comprises obtaining a sample of a subterranean formation from a well bore, subjecting said sample to evaporative conditions to obtain gasoline fraction hydrocarbons from said sample, adding a volatile carrier during said evaporation to aid separation or" said fractions, collecting from said sample the evaporates including said carrier as a concentrate, analyzing said concentrate to determine the amount of selected gasoline fraction hydrocarbons in said sample, and comparing specific hydrocarbons of said selected gasoline fraction hydrocarbons as an indication of commercially valuable oil in said formation.

17. A method in accordance with claim 16 wherein said selected gasoline fraction hydrocarbons include lower boiling hydrocarbons and high boiling hydrocarbons, and wherein the amount of low-boiling hydrocarbons is compared to the amount of high-boiling hydrocarbons in said sample as an indication of commercially valuable oil in said formation.

References Cited in the file of this patent UNITED ST TES PATENTS 2,694,923 Carpenter Nov. 23, 1954 2,713,010 Bonner July 12, 1955 2,733,135 Huckabay Ian. 31, 1956 2,767,320 Coggeshal-l Oct. 16, 1956 2,847,368 Worthington Aug. 12, 1958 2,854,396 Hunt Sept. 30, 1958 2,938,117 Schmidt May 24, 1960 OTHER REFERENCES Lichtenfels: Anal. Chem. vol. 27, p. 1510 to 1513, October 1955.

UNITED STATES PATENT oTrTcE QERTIHCATE @l fiQRREGllQN Patent N00 5 118 299 January 21 1964 Albert E Worthington It is hereby certified that error appears in the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

Column 2 line 641 for "metal read meta= g column 10 line 72 for "is" first occurrence read m it column 11 line 51 for "inc-erase" read we increase column 18 line 52 for "leng" read we long column 17 lines 37 and 38 for "value" each occurrence read valve column 18, line 56,, for "viscouse' read we viscous line 68 for "indicaitons' read indications line 73 for 'holefl" read ea hole column 19 line 47 for diagnositic" read me diagnostic D Signed and sealed this 16th day of June 1964a (SEAL) Attest:

ERNEST w sw EDWARD J. BRENNER Attesting Officer Commissioner of Patents 

1. A METHOD OF DETERMINING THE PRESENCE OF COMMERCIALLY VALUABLE OIL IN THE COURSE OF DRILLING A WELL BORE WHICH COMPRISES CIRCULATING DRILLING FLUID IN THE WELL BORE, WHEREBY SAID DRILLING FLUID CONTACTS THE EARTH FORMATION AT THE BOTTOM OF THE WELL BORE AND IS RETURNED TO THE WELLHEAD, TAKING A SERIES OF SAMPLES OF THE DRILLING FLUID RETURNS, SUBJECTING EACH OF SAID SAMPLES TO EVAPORATIVE CONDITIONS TO OBTAIN GASOLINE FRACTION HYDROCARBONS FROM SAID SAMPLE, ADDING A VOLATILE CARRIER DURING SAID EVAPORATION TO AID SEPARATION OF SAID FRACTIONS, COLLECTING THE EVAPORATES INCLUDING SAID CARRIER AS A CONCENTRATE, ANALYZING SAID CONCENTRATE TO DETERMINE THE AMOUNT OF AT LEAST ONE SELECTED GASOLINE FRACTION HYDROCARBON WHEREBY CHANGES IN THE SELECTED HYDROCARBON CONTENT IN SAID SERIES OF SAMPLES OF DRILLING FLUID RETURNS MAY BE CORRELATED WITH THE HORIZON OF THE FORMATION AT THE BOTTOM OF THE HOLE IN CONTACT WITH THE DRILLING FLUID SAMPLES INDICATING A CHANGE. 